1. Technical Field
The present invention relates to a reflector, a light source apparatus, and a projector, and particularly to a technology of a reflector used in a light source apparatus of a projector.
2. Related Art
A projector is required to be reduced in thickness of the entire apparatus in order to improve mobility and installability. In a lamp used as a light source of a projector, for example, an ultrahigh-pressure mercury lamp or other discharge lamps, a reflector that reflects light emitted from a light emitting portion has been used. To efficiently direct the light toward an illuminated surface, the reflector is often shaped into a surface of revolution having a spheroidal shape, a paraboloidal shape, or other shapes. The reflector needs to be large enough to efficiently direct the light toward an illuminated surface. Therefore, among the components of an illumination system of a projector, a reflector is particularly problematic in many cases in reducing the thickness of the projector. A light source apparatus including a reflector is required to be not only capable of efficiently directing the light toward an illuminated surface but also small in thickness. For example, JP-A-2007-93989 has proposed a technology for reducing the thickness of a light source apparatus including a reflector. In the technology proposed in JP-A-2007-93989, use of a cylindrically-shaped reflector allows reduction in thickness of the light source apparatus. Providing a plurality of reflection surfaces formed along the circumferential direction of a tubular body on the inner surface of the reflector allows light to be focused at a position on the central axis.
The reflection surfaces that focus light at a position on the central axis are provided on the surface of a corrugated structure, for example, a structure having a Fresnel shape that forms a Fresnel lens. The structure having a Fresnel shape has a rearward-facing surface provided between adjacent reflection surfaces. The rearward-facing surfaces are formed along the circumferential direction of the tubular body, as in the case of the reflection surfaces. Part of the light emitted from a light emitting portion is incident on the rearward-facing surfaces directly from the light emitting portion or after reflected off the reflection surfaces. The light incident on the rearward-facing surfaces is directed in a direction different from the direction toward an illuminated surface. The technology of the related art therefore disadvantageously makes it difficult to efficiently direct the light toward the illuminated surface.